Generally, in an air conditioner utilizing a refrigeration cycle, such as a refrigerator, a dehumidifier etc., pressurized refrigerant gas is in the tube which comprises part of the air conditioner device. The cooling cycle comprising compression, condensation, expansion and evaporation is operated successively so as to undergo the predetermined work. During the refrigerant gas circulation in the cycle, refrigerant gas leaks out through a cracked or defective part of the tube. Notwithstanding the loss of all or part of the refrigerant gas, the apparatus keeps on operating. Thus, the user can not immediately determine the leakage. This causes a waste of electricity in powering an inoperable device. Further, air gets into the tube through the leak whether or not in operation. Moisture in the air promotes oxidation or corrosion of the refrigerant tube, piston or cylinder in the compressor. This adversely effects to compression efficiency, endurance of parts etc.. Moreover, the formation of corrosion material clogs the capillary tube.